Cellular networks were originally developed to provide primarily voice services over circuit switched (CS) networks. However, the introduction of packet switched (PS) networks enables network operators to provide data services as well as voice services to users. Eventually, network architecture is expected to evolve toward all-IP networks capable of providing both voice and data services.
Currently, some UEs implement functionality that allows them to transition from communicating with a PS network, e.g., via an LTE network, to communicating with a CS network, e.g., via IS95/CDMA network. To accomplish this, the UEs enter an idle mode with respect to the CS network after registering with the CS network, and begin communicating over the PS network. While the UE is in the CS network idle mode, the CS network may provide the UE with services notifications via the PS network. For example, the CS network may alert the UE to an incoming call. Additionally, the UE may autonomously transition from the PS network to the CS network for a short period of time to perform some function associated with the CS network idle mode, or more specifically, some function associated with the Radio Resource Control (RRC) idle mode associated with the RAN that connects the UE to the CS network, such as to read a paging channel or perform a location update procedure. Once the CS operations are complete, the UE returns to the CS network idle mode and transitions back to communicating in the PS network.
Some UEs have two transceivers and can maintain connections to both the CS and PS networks. However, not all UEs can establish and maintain two different connections. Particularly, some UEs have only a single transceiver, and thus, must temporarily “tune out” of one network (e.g., the PS network) to communicate with the other (e.g., the CS network). For a UE, “tuning out” of the PS network can be problematic, particularly if there is data in the downlink buffers. More specifically, a UE would have to tune out of the PS network for up to two seconds to perform a task, and therefore would risk being dropped by the PS network.